Homo unius libri ('(a) man of one book') is a Latin phrase attributed to Thomas Aquinas by bishop Jeremy Taylor (1613–1667), who claimed that Aquinas is reputed to have employed the phrase "hominem unius libri timeo" ('I fear the man of a single book').
The poet Robert Southey recalled the tradition in which the quotation became embedded:
The phrase was in origin a dismissal of eclecticism, i.e. the "fear" is of the formidable intellectual opponent who has dedicated himself to and become a master in a single chosen discipline. In this first sense, the phrase was invoked by Methodist founder John Wesley to refer to himself, with "one book" (Latin: unius libri) taken to mean the Bible.[1] However, the phrase today most often refers to the interpretation of expressing "fear" of the opinions of the illiterate man who has "only read a single book".[2]
"I receive the written word as the whole and sole rule of my faith..... From the very beginning, from the time that four young men united together, each of them was homo unius libri... They had one, and only one, rule of judgement with which to regard all their tempers, words and actions; namely, the oracles of God." Wesley used it more publicly in the Preface to his collected sermons;
"He came from heaven; He hath written it down in a book. O give me that Book! At any price, give me the Book of God. I have it; here is knowledge enough for me. Let me be homo unius libri!"